Some vehicle crash situations may cause a force acting locally on one of the front wheels in a direction essentially perpendicular to the wheel. This force may cause a turning of the wheels. Since the wheels are connected to the steering wheel this may in turn result in a sudden steering wheel rotation. A sudden and unexpected rotation of the steering wheel may cause injury to the driver of the vehicle, for example in the hands and arms. Further, if a passive safety device, such as an airbag system, is mounted in the steering wheel, this rotation may result in a non-optimal engagement between occupant and airbag.
In current airbag systems the airbag protecting the driver is usually mounted in the central hub of the steering wheel and rotates with the steering wheel. An airbag cushion can be both symmetrical and asymmetrical in shape and is optimized to protect the driver. If the airbag rotates with the steering wheel during a crash, the symmetrical or asymmetrical airbag shape may instead introduce unintended forces on the drivers head/neck, this may lead to that the driver is unintentionally injured by the airbag or that he/she is guided in a direction offset from the airbag.
The above mentioned problems with the unintentional steering wheel rotation and airbag position are for example concerned in patent applications U.S. Pat. No. 7,931,296B2 and WO2008140633A1.
In U.S. Pat. No. 7,931,296B2 a steering arrangement includes a steering column and a steering wheel gear arranged offset from each other so that the torque from the steering wheel is transmitted to the steering column. An airbag module received in a steering wheel hub of the steering wheel is independently mounted such that it is not rotated together with the steering wheel by using the offset torque transmission structure interconnecting the steering wheel and steering column. Such configuration allows deployment of a cushion independent of shape with less risk of introducing unintended forces on head/neck.
In WO2008140633A1 it is disclosed a steering wheel assembly having a steering wheel armature, a hub portion and spokes. The hub portion is fixable to a conventional steering column shaft. The steering wheel assembly has a first drum supported on the steering column shaft, to freely rotate about only the axis of the steering column shaft. A second drum is freely rotatable with respect to the first drum about a second axis. The second axis is parallel to and spaced apart from or incident to the steering column shaft. Stationary support means are provided for supporting the second drum on the first drum. The support means provides a stationary support member, onto which an airbag module can be mounted, thus allowing the airbag module to remain stationary with respect to the vehicle during rotation of the steering wheel.
The above solutions require a reconstruction of the entire steering wheel and/or steering wheel column. A reconstructed steering wheel column may be difficult to insert in the tightly designed space in the vehicle and may require further redesign of the vehicle and vehicle parts. Further, a construction using a plurality of shafts or gears to keep the airbag module in a stationary position is cumbersome and complicated. Thus, it would be advantageous to provide a steering wheel assembly with a rotation countermeasure function requiring as little redesign of the steering column as possible.